Magnetoresistive random access memories (MRAMs) have certain beneficial characteristics such as being non-volatile, dense, and fast. These characteristics have made it very attractive for use as both a general purpose memory and as an embedded memory, i.e., a memory on-board a logic circuit such as a microcomputer. Putting such MRAMs into production has been difficult due to a number of factors. One of these is being able to consistently write a one and a zero that can be identified as such.
One technique for overcoming is the development of a toggle bit MRAM. Such is described in U.S. Pat. No. 6,545,906 B1, Savtchenko et al. In this case the MRAM is programmed by applying two timed magnetic signals so that the MRAM cell switches state regardless of its present state. A change from a logic one to a logic zero is achieved in the same way as a change from a logic zero to a logic one. This technique provides excellent consistency in writing both the logic one state and the logic zero state into the bit. Because the toggling of logic states is achieved by controlling the magnetic field in a bit, it is current in the write lines that create magnetic fields that must be controlled. Unfortunately, magnetic fields created by a particular write line current are not confined to the immediate vicinity of the write line. A portion of the magnetic field for a particular write line current can encroach on bits associated with neighboring write lines. These stray magnetic fields can cause erroneous toggling of bits associated with these neighboring write lines. Magnetic fields may be influenced by current conduction and the direction thereof.
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